13,703
edits
Changes
m
no edit summary
'''Sour Worting''' is a process in which [[Lactobacillus]] is given a "head start", pitched before the yeast so that it will be able to produce significant amounts of lactic acid before the saccharomyces completes the main fermentation. There are several variations on this method, including souring in the primary fermenter, souring in a secondary vessel, or even souring in the boil kettle itself. There are also various methods of inoculating the wort with Lactobacillus. Finally, the brewer has the option of pasteurizing the wort by heating it to kill the Lactobacillus before adding the yeast for the main fermentation. Many brewers prefer this process over [[Sour Mashing]] because it can be easier to control, and when implemented properly it produces a clean sour beer in a short amount of time. The possibility of pasteurizing the soured wort also makes this a good method for making sour beers with a lot of residual malt sweetness (e.g. sour barley wines), and should also make it attractive to brewers who are concerned about infection issues in their cold side equipment (equipment that is used post-boil) <ref>[http://sourbeerblog.com/fast-souring-lactobacillus/ Miller, Matt. Dec 20, 2014. "Fast Souring with Lactobacillus – Best Practices, Sensory, & Science". Sour Beer Blog.]</ref>. When sour worting, some brewers first [[Sour_Worting#How_to_Pre-Acidify|lower the pH of the wort to 4.5-4.8 ]] before pitching Lactobacillus. This has sometimes been found to help the head retention of the beer. For more information, see the [[Lactobacillus#Foam_Degradation|Lactobacillus page section on Foam Degradation]].
Important note regarding aluminum pots: souring in an aluminum vessel may strip the aluminum of the protective oxide layer. The oxide layer is only stable at a pH of 4.5 - 8.5. Therefore, kettle souring in an aluminum pot is generally not recommended <ref>[http://www.pfonline.com/articles/aluminum-surface-finishing-corrosion-causes-and-troubleshooting Aluminum Surface Finishing Corrosion Causes and Troubleshooting. W. John Fullen, Boeing Research and Technology & Jennifer Deheck, Boeing, Seattle, Washington, USA. 10/17/2014.]</ref>.
The brewing process is the same for any all grain batch up until the first wort and sparge runnings are collected into the boil kettle. The temperatures that a typical mash out/sparge reach should be enough to pasteurize the wort <ref name="pasteurization">[http://science.howstuffworks.com/life/cellular-microscopic/pasteurization4.htm Heat pasteurization]</ref>. Once all of the wort is collected in the boil kettle, the wort is chilled to around 80-120°F (37-48°C), depending on the [[Lactobacillus]] culture that is being used. Once chilled to the temperature that is appropriate, the wort in the kettle is inoculated with a culture of Lactobacillus.
There are various ways of inoculating the wort. A reliable method is pitching a pure culture of Lactobacillus, or a blend of Lactobacillus cultures. Alternatively, a handful of unmilled malted barley can be added to the kettle for inoculation instead of a pure culture, since the husks of grain carry many microorganisms. If unmilled grain is added, it is recommended to fill the head space of the kettle with CO2 because oxygen can encourage off flavors such as rancid cheese from [[Butyric Acid]] and/or [[Isovaleric Acid]], which are produced by microbes that are naturally present on the grain. Keeping the temperature between 113-120°F (45-48.8°C) will encourage the Lactobacillus resident on the grain and will discourage other bacteria. Lowering the pH of the [[Sour_Worting#How_to_Pre-Acidify|wort to under 4.4 5]] will also discourage many other bacteria from thriving in the wort during the incubation period. Consider [[Alternative Bacteria Sources]] for more reliable approaches to using "wild" Lactobacillus, or Lactobacillus from sources other than yeast labs.
If a pure culture of Lactobacillus bacteria is used it is ideal but not necessary to fill the head space of the fermenter with CO2 gas (some brewers have reported that this will help reduce sulfur in the finished beer). The kettle should be held at the desired temperature for 24-72 hours (in some cases longer, but no longer than 5 days). Depending on the strain of Lactobacillus, and the desired sour level, the time of incubation is ultimately a variable that is up to the brewer (see the [[Lactobacillus]] page for suggested temperatures and times for specific strains). The kettle lid should be firmly in place and optionally sealed with plastic wrap so that other microorganisms do not get in. Potential for formation of [[Butyric Acid]] and [[Isovaleric Acid]] when using only a pure culture is extremely slight to none assuming no other microbes are allowed inside the kettle.